Apparatus for producing fine fibers



Nov. 12, 1968 E. CROMPTON APPARATUS FOR PRODUCING FINE FIBERS OriginalF'iled June 16, 1965 INVENTOR THOMAS E. CROMPTON I BY Wa -W UnitedStates Patent 3 409,938 APPARATUS FOR PRODUCING FINE FIBERS Thomas E.Crompton, Cary, N.C., assignor to Monsanto Company, St. Louis, Mo., acorporation of Delaware Original application June 16, 1965, Ser. No.464,477. Divided and this application June 23, 1967, Ser. No.

Claims. (Cl. 18-2.6)

ABSTRACT OF THE DISCLOSURE This application is a division of Ser. No.464,477 filed June 16, 1965.

Heretofore, fine fibers of synthetic organic polymers have been made byprocesses which involve the action of a high velocity jet of gas on amolten polymeric material. In accordance with these known processes, amolten polymer is extruded through one or more orifices into a gasstream of high velocity. The gas stream acts to break up the moltenstream into small particles, which solidify, and are carried away by thegas stream. While these processes have been successful to some extent, amajor problem encountered is the lack of uniformity in the shape andsize of the fibers produced. When the gas stream acts on the moltenpolymer stream the particle forms vary greatly in size. Furthermore,when these particles are solidified, globules or beads are formed alongwith the fibers due in part to the difference in size and also due tothe fact that some solidification occurs as the gas stream contacts themolten polymer.

Additionally, these previously known processes have been somewhatrestricted in their application in the use of a molten polymer feed. Inthese previously known processes, the use of a polymer solution as afeed is extremely difficult due to the low viscosity of the solution andalso due to the difficulties encountered in solvent removal.

It is therefore an object of this invention to provide a method for theproduction of uniform fine fibers of a synthetic organic polymer.

It is a further object of this invention to provide a method for theproduction of uniform fine fibers of a synthetic organic polymer from asolution of said polymer.

It is a further object of this invention to provide apparatus for theproduction of uniform fine fibers of a synthetic organic polymer from asolution of said polymer.

Other objects will become apparent from the following description.

Briefly, the method of the present invention involves feeding a solutionof a synthetic organic polymer onto the internal, concave face of arotating conoid surface, allowing said solution to substantially coversaid internal concave face and be discharged as elongated droplets fromthe periphery of said surface by the centrifugal force resulting fromthe rotation of said surface, surrounding the periphery of said surfacewith an annular gas stream flowing substantially parallel with the axisof rotation of said surface, entraining the discharged droplets in saidgas stream, removing solvent from said droplets by the action of saidgas stream thus forming fine fibers of said polymers in said gas stream,and recovering said fibers formed in said stream.

The process will be more fully understood with reference to theaccompanying drawings in which:

FIGURE 1 is a perspective view of the fiber-forming apparatus of thisinvention;

FIGURE 2 is a sectional top view of the apparatus shown in FIGURE 1 atline 2-2;

FIGURE 3 is a perspective view of a form of apparatus used to collectthe fibers formed by the present invention, and

FIGURE 4 is a view of a preferred form of the conoid disc used in thepresent invention.

There is shown in FIGURE 1 a typical arrangement of the apparatus usedto carry out the present invention. A solution of a synthetic organicpolymer from source 1 is passed via line 2 and pump 3 through tubularfeeding means 4 onto the internal concave face of conoid disc 5 throughthe aperture 6. The pump 3 provides constant pressure to the solutionthus allowing the solution to essentially cover the concave face of disc5. The disc 5 is rotatably mounted in casing 7 and is rotated by chaindrive 8 and motor 9. In order to produce the uniform fine fibers by themethod of the present invention, the conoid disc should be capable ofrotating at speeds between 1000 r.p.m. and 7000 r.p.m., preferablybetween 2000 and 4000 r.p.m. A gas, for example, air, from a source notshown, is forced by pump 10 through heating means 11 and line 12 and outvaned annular opening 13 into enclosure 14. The polymer solution isdischarged from disc 5, by the centrifugal force resulting from itsrotation, in the form of elongated droplets which are picked up in thegas stream exiting from opening 13, are carried through enclosure 14 anddeposited on gathering means 15, which is shown in the form of a screen.During the passage of the droplets from disc 5 to screen 15, the actionof the gas stream removes the solvent from the polymer solution thusforming fine fibers which are deposited on screen 15. Screen 15 ispreferably in the form of an endless belt which is moved by drive means17 and motor 18 in a direction perpendicular to the axis of rotation ofdisc 5. As'the screen moves out of enclosure 14 the fibrous mat 16formed thereon is removed and taken up, for example, on take up roll 19driven by motor 20. The solvent remaining in the gas stream passesthrough the screen and is directed by baffles 22 and 23 shown in FIGURE2, to solvent collection means 21.

While FIGURE 1 shows the removal of the fibers from the gathering meansin the form of a mat, it is also possible, and in some cases desirable,to remove the fibers in the form of a yarn. This may be done by theapparatus shown in FIGURE 3 wherein air jets 24 serve to decrease thewidth of mat 17 as it passes over roll 19. The fibers are furthercompacted by passage through guide 25, over roll 26 and through guide 25(a). The yarn 27 is thence taken up on bobbin 28.

Rotating disc element 5 is more clearly shown in FIG- URE 4. Thiselement as shown in FIGURE 4 is composed of tubular neck portion 5(a)and conoid discharge surface 5(b) flaring outwardly therefrom. As shownin FIGURE 4, aperture 6 must be located centrally in disc 5. This allowsuniform distribution of the polymer solution over the entire face of thedisc. It is also desirable that the disc 5 terminate in a sharpedgeperiphery 29. This allows the solution to leave the face of the disc inelongated droplets which pass into the surrounding gas stream and alsoserves to prevent the solution from back flowing over the convex side ofdisc 5. In accordance with a preferred method of the present invention,the polymer solution is allowed to cover the inside surface of tubularneck portion 5(a) prior to its passage through aperture 6 onto dischargesurface 3 5 (b). This insures a more even distribution of the solutiononto the discharge surface.

Any synthetic organic polymer that is solution-spinnable may be used inthe process of the present invention. Thus, in accordance with thepresent invention, fibers may be made from polyacrylonitrile,polycarbonates, polyurethanes, and other like polymers which may bedissolved in a solvent and fed to the rotating disc. Likewise, mixturesof fibers may be spun in accordance with the process of the presentinvention either by admixing the solutions prior to their introductionthrough the feeding means, by having a plurality of feeding meansthrough the aperture of the conoid disc, or by providing a plurality ofdiscs on the same shaft. The preferred polymer for use in the method ofthe present invention comprises acrylonitrile and copolymers thereof.

Due to obvious economic advantages, itis preferred in accordance withthe process of the present invention to employ air as the annular gasstreamsurrounding the periphery of the rotating disc. Since it is highlydesirable that most of the solvent be removed from the polymer prior toits reaching the target, it is preferred to heat the incoming air streamin order to achieve this end. It has been found that an air streamheated to a temperature of between about 100 C. and about 350 C.,preferably 250 C. to 300 C., serves to insure solvent removal from thefibers.

It is necessary that the annular gas stream be traveling at a velocitysufiicient to overcome the centrifugal force imparted to the elongateddroplets by the rotating cone and entrain the droplets of solution tothe gathering means. Furthermore, the velocity must be sufiicient toremove the solvent from the droplets. A gas stream velocity of between1500 feet per minute and 6000 feet per minute has been found necessaryfor this purpose with the preferred gas velocity lying between theranges of 2000 feet per minute and 4000 feet per minute.

The shape of disc 5 is preferably that of a cone although other shapes,for example, saucer-like shapes may be equally well employed. The onlyrequirement is that disc 5 be of a shape which allows uniformdistribution of the polymer solution over the entire face thereof.

It has been found that the concentricity of the disc is an importantfactor in the successful operation of the process and apparatus of thisinvention. That is, the peripheral edge of disc 5 must be substantiallycompletely concentric with its axis of rotation and with the peripheryof aperture 6. When disc 5 is out-of-round to any substan tial degree,the polymer solution does not discharge evenly over its entireperipheral surface and globule formation results.

Fibers made in accordance with the process of the present invention areessentially uniform in shape and size. Bead formation is essentiallyeliminated and the diameters of the fibers range from about 5 microns toabout 0.1 micron with the average diameter being between 1 and 2microns. The fibers produced by the present invention have outstandingproperties which make them useful for paper products, laminates,absorbent pads,

filters, insulation and the like.

I claim:

1. Apparatus for producing fine fibers of a synthetic organic polymercomprising a conoid dischaving'a convex surface and concave surface,means to rotate said'disc about a substantially horizontal axis,anaperture positioned centrally in said disc, tubular feeding meansextending outwardly from said convex surface and adapted to dischargeliquid to the concave surface of said disc through said aperture,pressure means operative to apply pressure to the polymer solution insaid tubular feeding means, means surrounding the periphery,of s aiddisc to provide a heated annular gas stream flowing substantiallyparallel to the axis of said disc, collection means in said gas streamadapted to collect solvent from said gas stream and gathering meanspositioned between said'collection means and said disc for removingfibers from said gas stream.

2. Apparatus as described in claim 1 wherein said gathering meanscomprises 'a movable screen, means to move said screen in a directionperpendicular to the axis of rotation of said disc and m'eans'associatedtherewith to remove fibrous materials from said screen.

3. Apparatus as described in claim 1 wherein said disc is cone-shaped.

4. Apparatus'for producing fine fibers of a synthetic organic polymercomprising a cone-shaped disc having a concave surface and a convexsurface, the concave surface of said disc being uniform and terminatingin a sharpedged periphery, an aperture located centrally in said disc,means to rotate said disc about a substantially horizontal axis, feedingmeans extending outwardly from said convex surface and adapted todischarge liquid through said aperture and onto said concave surface,pressure means adapted to apply pressure to the solution in said feedingmeans, means surrounding said disc for providing a heated annular gasstream flowing past said edge in a direction substantially parallel tothe axis of rotation of said disc, collection means associated with saidgas stream adapted to collect solvent from said stream and gatheringmeans located between said collecting means and said disc adapted toremove fibers from said stream.

5. Apparatus as described in claim 4 wherein said gathering meanscomprises a movable screen, means to move said screen in a directionperpendicular to the axis of rotation of said disc and means associatedtherewith adapted to remove fibers from said screen in the form of ayarn.

References Cited UNITED STATES PATENTS 2,217,235 10/1940 Rieser 182.6 XR2,238,204 4/1941 Woods 182.6 XR 2,333,218 11/1943 Von Pazsiczky 182.6 XR3,097,085 7/1963 Wallsten l82.6 XR 3,317,954 5/1967 Crompton l82.6

WILLIAM J. STEPHENSON, Primary Examiner.

